Hypothesis 1: fracture and tendon damage

When assisting in bovine dystocia, forced fetal extraction is often used to overcome maternal-fetal misproportion.  Chains are used and are attached above and below the metacarpal-phalangeal joint to provide a stable but non-focal force.  The chains can then be attached to a calf jack that provides increased tension to remove the calf from the dam.  If the chains are not attached to the calf and/or the calf jack properly a disproportionate amount of force and stress may be applied to a specific leg or joint.   This force can fracture a limb and possibly injure tendons.  If a fractured limb is set incorrectly, delayed union may occur.  This would explain the crepitance and crooked leg that this calf is exhibiting.  If tendons are injured, they heal by scarring and contracture.  Involvement of the extensor tendons would explain the hyperextension that the owner describes and that we see on physical exam.  
	One consequence of a fractured leg is the formation of a sequestrum, or a fragment of bone that is no longer attached in any way to the rest of the bone.  This would cut off the blood supply to this piece of bone and reduce it's immunocompetence.  Any bacteria that would have been introduced via wound contamination can cause a focal osteomyelitis characterized by the draining tract and purulent exudate noted on the dorsomedial aspect of the metacarpus.
	Hyperextension can also occur if there is a prolonged cast on the leg, because the deep digital flexor tendon and surrounding soft tissue is relaxed and weak.  This calf had a cast on his leg for a total of 2 months; if sufficient care was not taken to stretch the limb during cast changes, it could result in the weakness of the flexor tendons and hypersextension of the toes.
	The heavy bandage may have been applied too tightly, and caused pressure necrosis of the thin skin of the distal limb of the calf.  The lower limbs of cattle have very little underlying soft tissue structures to help cushion the bandage, so it is rather susceptible.  We see as evidence the sloughing of the skin after two weeks of the bandage.
	The radiographs should show a non-united fracture, a sequestrum surrounded by an involucrum, and soft tissue swelling.  The neurological exam should be normal, and depending on the extent of the osteomyelitis, we might see a inflammatory leukogram.